This invention relates to the isolation of antibody molecules directed against self antigens, e.g. human antibodies directed against human self antigens. Phage display technology for selection of antibody molecules was described in WO92/01047, PCT/GB92/00883, PCT/GB92/01755 and GB9206372.6. The applicants have realised that antibodies directed against self antigens can be isolated using phage display technology.
Human antiself antibodies are of particular value for in vivo therapeutic and diagnostic purposes, since they avoid the problems arising from the antigenicity of foreign, e.g. mouse antibodies. The most useful human antibodies for therapy are those directed against cell surface molecules, such as receptors, adhesins and integrins, and those directed against circulating biological effector molecules, such as hormones, growth factors and cytokines. It has been extremely difficult to obtain human antibodies against such self antigens. This invention provides a powerful way of obtaining such antibodies.
It is a demanding task to isolate an antibody fragment with specificity against self antigen. Animals do not normally produce antibodies to self antigens, a phenomenon called tolerance (G. J. Nossal Science 245 147-153, 1989). Autoimmune diseases may result from a breakdown in tolerance. In general, vaccination with a self antigen does not result in production of circulating antibodies. It is therefore difficult to raise antibodies to self antigens, particularly in humans. It is possible to raise antibodies that recognise human antigens in an animal such as a mouse, especially if the human antigen is not too closely related to any equivalent in the animal. If a human antibody is then required it is necessary to xe2x80x98humanisexe2x80x99 the anti-body, e.g. by CDR grafting (patent GB2188638B).
Phage antibody technology as described in (WO92/01047) offers the ability to isolate such human antibodies directly. In this application, we demonstrate for the first time that antibodies against self-antigens can be isolated from phage libraries derived from, for example, nonimmunised sources and from libraries prepared by synthetic recombination of V-gene sequences, preferably recombination of VH with, DH and JH, and VL with JL sequences. These antibodies are specific for their antigen. This application shows that single libraries derived in this manner can act as a source of both foreign and self antigens and opens up the prospect of a large, universal library to isolate antibodies to any antigen.
It was disclosed in patent application WO92/01047 that antibody fragments can be displayed on the surface of bacteriophage and that they will bind antigen. Antibody fragments can be directly selected using this characteristic. This ability to isolate antibody fragments (Fab, Fv, scFv and VH) using their display on the surface of filamentous bacteriophage has opened up the prospect of the isolation of antibody specificities (i.e. antibodies directed against a particular antigen) that were difficult or impossible to isolate previously. In particular WO92/01047 demonstrates that antibody specificities can be isolated from a human who has not been specifically immunised (xe2x80x98unimmunisedxe2x80x99), even specificities for antigens such as 2-phenyl-5-oxazolone to which humans will not normally be exposed.
In embodiments of this invention, natural or synthetic antibody repertoires derived from a species of mammal, such as human, mouse, rat, sheep, pig, goat, horse or other, are displayed on the surface of a replicable genetic display package (rgdp) and the binding specificity for self is selected by binding to self antigen. In this process, the V gene repertoires are derived from V genes rearranged in vitro or in vivo and or by mutation of (a) rearranged V gene(s). A key feature of the V gene repertoires is that they are extremely diverse in sequence, usually in excess of 106 different members. Indeed it is possible that a sufficiently large library may provide a source of specificities directed against any self antigen. The V-gene repertoires are cloned into the rgdp (for example a filamentous phage vector) such that antibody repertoires are displayed on the surface of the rgdp. The rgdps encoding rare antibody specificities binding to antiself, may be selected by virtue of binding to the self antigen. The antibody repertoires may be cloned in a single replicon or a dual replicon format as described in WO92/01047 and PCT/GB92/00883.
The V genes may be cloned into the genetic material of the rgdp, and expressed as single domains, for example single heavy chain variable domains, so called single domain ligands or xe2x80x9cdAbsxe2x80x9d (see WO90/01544), or as associated antibody heavy and light chain variable domains.
The two domains could be displayed as separate polypeptide chains (linked as in Fab fragments through non-covalent association of domains and/or disulphide bonds), or as part of the same chain (single chain Fv fragments where the two domains are contained within the same polypeptide chain).
In WO92/01047 and examples 1 to 8 of this application we have used fusion of antibody fragments to gene 3 protein of filamentous bacteriophage for display and selection of antibody fragments. An alternative approach would be to fuse antibody fragments to gene 8 protein or other surface molecules of filamentous bacteriophage.
Isolation of human antibodies directed against human antigens is a demanding task. There are only a limited number of human antigens against which circulating human antibodies are naturally found. Antibodies are present directed against non-self antigens of human origin. Antibodies directed against human blood group B have been isolated from a phage display library prepared from subjects of blood group O (J. D. Marks et al, J. Mol. Biol. 222 581-597, 1991), which recognise the blood group B antigen as foreign.
This invention is concerned with a general method for the isolation of antibodies directed against self antigens which are specific for the antigen concerned. Many patients show significant concentrations of circulating autoantibodies. It is estimated that 10 to 30% of B lymphocytes in normal, healthy individuals are engaged in making autoantibodies (I. R. Cohen and A. Cooke Immunol. Today 7 363-364, 1986). However, the xe2x80x98natural autoantibodiesxe2x80x99 produced do not lend themselves to therapeutic use as they are often IgM, low affinity and polyreactive (P. Casali and A. L. Notkins Ann. Rev. Immunol. 7 515-531, 1989; S. Avrameas Immunol. Today 12 154-159). An immune response against self can arise in autoimmune disease or after infections and a few monoclonal antibodies directed against self antigens have been isolated from patients with autoimmune disease (K. James and G. T. Bell J. Immunol. Methods 100 5-40, 1987). These autoantibodies are frequently specific, but may bind to only a limited range of epitopes on the antigen (M. Bouanani et al Arthritis Rheum. 34 1585-1593, 1991).
The preparation of V gene libraries derived from the mRNA of plasma cells secreting IgG (or IgM) antibody may thus lead to the isolation of antibody fragments derived from autoantibodies. For instance, anti-self antibodies might be isolated from patients with autoimmune diseases, for example anti-acetylcholine receptor antibodies would be expected to be isolated from antibody repertoires made from the IgG mRNA of myasthenia gravis patients. For example, an antibody fragment specific for human thyroid peroxidase has been isolated from a bacteriophage lambda library from a patient with thyroid autoimmune disease (S. Portolano et al Biochem. Biophys. Res. Commun. 179 372-377, 1991). This however required extensive screening of 200,000 plaques to obtain one clone. In addition, this library was derived from thyroid tissue, a procedure not readily applicable in most instances.
In contrast, the power of selection available using the phage system, demonstrated in WO92/01047 allows the ready isolation of autoantibodies from the IgM mRNA of peripheral blood lymphocytes of a donor without disease. We show in example 2 that antibodies binding to human thyroglobulin (which can be found in the sera of people with or without symptomatic autoimmune disease), can be isolated from phage repertoires prepared from unimmunised humans. One would not expect necessarily to be able to obtain antibodies to human thyroglobulin by immunising a human with human thyroglobulin, notwithstanding the presence of thyroglobulin autoantibodies in many people. Autoantibodies against thyroglobulin in normal sera have been reported often to have a high degree of polyreactivity (S. Avrameas, 1991 supra). In contrast, those which are isolated using a method according to the present invention involving phage antibody technology, see example 2 for instance, are specific for thyroglobulin.
In this application, we also demonstrate that even antibodies against human tumour necrosis factor-xcex1 can be isolated as described in example 1 from the same library as the antibodies directed against thyroglobulin. Many self antigens do not have detectable associated circulating autoantibodies. Further, example 3 shows the isolation of antibodies against the self antigens mucin, carcinoembryonic antigen (CEA) and CD4, antibodies to which have not been reported in normal sera. Moreover, these antibodies are specific, whereas there is often a high degree of polyreactivity in natural autoantibodies which can sometimes be found. The vast majority of self antigens do not have detectable associated circulating autoantibodies. Thus the isolation of antiself antibodies as described in this invention opens the prospect of the direct isolation of human antibodies binding to human antigens for a number of purposes such as antibodies which bind to circulating hormones to block, modify or potentiate their action or antibodies that bind to cell surface antigen for imaging or killing for example of cancer cells.
The origin of the V genes that contribute to anti-self antibodies isolated from phage display libraries is not clear. Tolerance to self antigens by the immune system (preventing the generation of antibodies directed against them) is mediated by either clonal deletion or functional inactivation (anergy) of self-reactive B lymphocytes (D. A. Nemazee and K. Burki Nature 337 562-566, 1989; C. C. Goodnow et al Nature 334 676-682, 1988; S. B. Hartley et al Nature 353 765-769, 1991; D. M. Russell et al Nature 354 308-311, 1991). In either case little circulating anti-self antibody is detectable for most antigens. However, in the case of anergy, functionally inactivated self-reactive cells from the B cell lineage persist in peripheral lymphoid organs leading to B cells in circulation. These rare lymphocytes with anti-self specificity may provide heavy or light chain partners (or even both) for phage antibodies with anti-self specificities. Alternatively, such anti-self specificities may arise from the combination in the library of a VH domain with a VL domain to give a specificity that is normally deleted if it occurs in nature. For this reason, combinatorial libraries and xe2x80x98chain-shuffledxe2x80x99 libraries such as described in patent applications WO92/01047 may be a particularly rich source of anti-self antibodies. A selection procedure of great power, such as that provided by phage antibodies, is required to obtain such rare anti-self antibodies.
The degree of somatic mutation observed in antiself antibody fragments isolated by phage technology in this application indicates that some have germ line sequences and have therefore arisen from virgin B cells. Other antibodies isolated by phage antibody technology in this application show somatic hypermutation indicating that the V genes have been stimulated by antigen, either a foreign cross reactive antigen or other foreign antigens. In both cases the antibody fragments isolated using phage technology will usually be a combination of VH and VL domains not originally present in the B lymphocytes and the power of phage technology, as described in this application enables their isolation.
According to the present invention there is provided a method of obtaining a member of a specific binding pair (sbp member), which sbp member has an antigen binding site with binding specificity for an antigen which is a self antigen of a species of mammal, the method comprising:
(a) providing a library of replicable genetic display packages (rgdps), each rgdp displaying at its surface an sbp member, and each rgdp containing nucleic acid with sequence derived from said species of mammal and encoding a polypeptide chain which is a component part of the sbp member displayed at the surface of that rgdp;
(b) selecting, by binding with said self antigen, one or more sbp members with binding specificity for said self antigen.
The polypeptide component part encoded by the nucleic acid in each rgdp may be a VH or VL domain of an antibody, or any part of an antibody which, either alone or in combination with one or more other component parts, forms an antibody fragment which is capable of binding an antigen. Examples of polypeptide chains which may be used as component parts of an sbp member as described above therefore include, in addition to VH and VL domains, VLCL, VHCH1, scFv fragments, Fab fragments and so on.
Each said sbp member displayed at the surface of an rgdp may be an antibody fragment comprising a VH domain and a VL domain.
Each antibody fragment may be a scFv fragment, a Fab fragment, a Fv fragment consisting of the VL and VH domain of a single arm of an antibody, a single domain binding-ligand consisting essentially of or comprising a heavy-chain variable domain (Fd), or any other fragment which has the capability of binding an epitope or antigen.
The step of providing a library of rgdps may comprise:
combining (i) a first polypeptide chain component part of an sbp member fused to a component of a rgdp which thereby displays said first polypeptide chain component part or population thereof at the surface of rgdps on expression in a recombinant host cell organism, or a population of such a first polypeptide chain component part fused to a said component of a rgdp, with (ii) a second polypeptide chain component part of an sbp member or a population of such a second polypeptide chain component part, to form a library of sbp members displayed at the surface of rgdps;
at least one of said first or second polypeptide chain component part or populations thereof being encoded by nucleic acid which is capable of being packaged using said component of an rgdp.
The step of providing a library of rgdp may comprise:
expressing in a recombinant host organism a first polypeptide chain component part of an sbp member or a population of such a first polypeptide chain component part, fused to a component of an rgdp which thereby displays said polypeptide chain component part at the surface of rgdps;
combining said first polypeptide chain component part or population with a second polypeptide chain component part of an sbp member or a population of such a second polypeptide chain component part, to form a library of rgdps each displaying an sbp member at its surface, at least one of said polypeptide chain component parts being expressed from nucleic acid which is capable of being packaged using said component of an rgdp.
Where the sbp member is an Fab fragment the first and second polypeptide chain component part may be a polypeptide consisting of a VL and a CL domain, and the second polypeptide chain component part a polypeptide consisting of a VH and a CH1 domain.
The combining of first and second polypeptide chain component parts or populations thereof may be at the nucleic acid level with expression vectors each having introduced therein a sequence encoding a first component part and a sequence encoding a sequence component part. On the other hand, the combining may be at the polypeptide level with first component parts not being expressed from the same vectors as second component parts. Indeed, one or other of the first and second component parts may be provided as a soluble library. Details of various formats which may be employed are given in WO92/01047 and PCT/GB92/00883.
The step of providing a library may comprise:
combining (i) nucleic acid which encodes a first polypeptide chain component of an sbp member fused to a component of a rgdp or a population of such a first polypeptide chain component part fused to a component of a rgdp, with (ii) nucleic acid encoding a second polypeptide chain component part of an sbp member or a population thereof, to form a library of nucleic acid, nucleic acid of said library being capable of being packaged using said component of an rgdp;
expressing in a recombinant host organism said first polypeptide chain component part fused to a component of a rgdp or population thereof and said second polypeptide chain component part of an sbp member or a population thereof, to produce a library of rgdps each displaying at its surface an sbp member and containing nucleic acid encoding a first and a second polypeptide chain component part of the sbp member displayed at its surface. Readers are urged to consult WO92/01047, in particular, if further details of any method described herein are desired.
In one embodiment of the present invention both first and second polypeptide chain component parts or populations thereof are expressed from nucleic acid capable of being packaged using said component of an rgdp. This might be when the component parts together form a Fab fragment or, more usually, when each said sbp member displayed at the surface of an rgdp is an scFv antibody fragment.
In one embodiment, each said second polypeptide chain component part or population thereof may be expressed from nucleic acid separate from nucleic acid from which said first polypeptide chain component part or population thereof is expressed. The nucleic acid encoding the first polypeptide chain component part may be on the same expression vector as the nucleic acid encoding the second polypeptide chain component part, but separate from it so that, for example, Fab fragments are produced. Alternatively, the nucleic acid encoding the first polypeptide chain component part may be on a different expression vector from the nucleic acid which encodes a second polypeptide chain component part. Where a first and second polypeptide chain component part are both encoded on the same expression vector then they may be expressed as scFv fragments, where a VH domain is joined to a VL domain by a polypeptide linker, so that each scFv is a single polypeptide chain.
Each sbp member displayed at the surface of an rgdp is an Fab antibody fragment.
The nucleic acid may be derived from, e.g. rearranged V genes of, an unimmunised mammal, for example a mouse, rat, rabbit, sheep, pig, horse, goat, dog or human. Preferably the species of mammal is human, since it is most difficult to obtain antibodies which recognise (i.e. bind specifically) human self antigens.
The nucleic acid may be derived from a library prepared by artificial or synthetic recombination of V-gene segments, which may be germ-line v-gene sequences. The library may be totally synthetic.
Sbp members selected in (b) displayed at the surface of rgdps may be selected or screened to provide an individual sbp member or a mixed population of said sbp members associated in their respective rgdps with nucleic acid encoding said sbp member or a polypeptide chain thereof. Rgdp phage displaying sbp members selected in (b) may be grown to increase their numbers before any subsequent further selection or screening. Nucleic acid which encodes a selected or screened sbp member and which is derived from an rgdp which displays at its surface a selected or screened sbp member may be used to express an sbp member or a fragment of derivative thereof in a recombinant host organism.
The present invention encompasses any method wherein nucleic acid from one or more rgdps selected from the library by binding with a self antigen is taken and used to provide encoding nucleic acid in a further method (according to any embodiment of the present invention or not) to obtain an individual sbp member or a mixed population of sbp members, or encoding nucleic acid therefor.
The expression end product, selected sbp member, may be modified to produce a derivative thereof.
The expression end product or derivative thereof may be used to prepare a therapeutic or prophylactic medicament or a diagnostic product.
The present invention also encompasses antibody fragments, derivatives thereof, including whole antibodies and fusions with enzymes, obtained using any method described herein according to the present invention.
According to an aspect of the present invention, there is provided use, in any method according to any embodiment of the present invention described herein, of a kit comprising a library of vectors each comprising nucleic acid which is capable of being packaged in rgdps and which encodes a polypeptide chain component part of an antibody for display at the surface of rgdps.
There is also provided by the present invention use, in any method according to any embodiment of the present invention described herein, of a kit comprising a library of rgdps each containing nucleic acid encoding at least one polypeptide chain component part of an antibody.
The present invention provides generally a method for producing a replicable genetic display package (rgdps) or population of such rgdps, which method comprises the steps of:
(a) inserting a nucleotide sequence encoding a binding molecule which is a member of a specific binding pair and an anti-self antibody, within a viral genome;
(b) culturing the virus containing said nucleotide sequence so that said binding molecule is expressed and displayed by the virus at its surface.
The present invention also provides a method for selecting a rgdp specific for a particular self-antigen epitope which comprises producing a population of such rgdps and the additional step of selecting for said binding molecule which is an anti-self antibody by contacting the population with said epitope so that individual rgdps with the desired specificity may bind to said epitope. The method may comprise one or more of the additional steps of: (i) separating any bound rgdps from the epitope; (ii) recovering any separated rgdps and (iii) using the inserted nucleotide sequences from any separated rgdps in a recombinant system to produce the binding molecule separate from the virus. The selection step may isolate the nucleotide sequence encoding the binding molecule of desired specificity, by virtue of said binding molecule being expressed in association with the surface of the virus in which said encoding nucleic acid is contained.
The present invention also provides a method of producing a multimeric member of a specific binding pair (sbp) which is an anti-self antibody, which method comprises:
expressing in a recombinant host organism a first polypeptide chain of said sbp member or a genetically diverse population of said sbp member fused to a component of a secreted replicable genetic display package (rgdp) which thereby displays said polypeptide at the surface of the package, and expressing in a recombinant host organism a second polypeptide chain of said multimer and causing or allowing the polypeptide chains come together to form said multimer as part of said rgdp at least one of said polypeptide chains being expressed from nucleic acid that is capable of being packaged using said component therefor, whereby the genetic material of each said rgdp encodes a said polypeptide chain.
Both said chains may be expressed in the same host organism.
The first and second chains of said multimer may be expressed as separate chains from a single vector containing their respective nucleic acid.
At least one of said polypeptide chains (or polypeptide chain component parts) may be expressed from a phage vector.
At least one of said polypeptide chains may be expressed from a phagemid vector, the method including using a helper phage, or a plasmid expressing complementing phage genes, to help package said phagemid genome, and said component of the rgdp is a capsid protein therefor. The capsid protein may be absent, defective or conditionally defective in the helper phage.
The method may comprise introducing a vector capable of expressing said first polypeptide chain, into a host organism which expresses said second polypeptide chain in free form, or introducing a vector capable of expressing said second polypeptide in free form into a host organism which expresses said first polypeptide chain.
Each of the polypeptide chain may be expressed from nucleic acid which is capable of being packaged as a rgdp using said component fusion product, whereby encoding nucleic acid for both said polypeptide chains are packaged in respective rgdps.
The fusions may be expressed in the absence of the rgdp display component, perhaps capsid, expressed in wild-type form.
The capsid protein may be absent, defective or conditionally defective in the helper phage.
The host cell may be a mutator strain which introduces genetic diversity into the sbp member nucleic acid.
The rgdp may be a bacteriophage, the host a bacterium, and said component of the rgdp a capsid protein for the bacterophage. The phage may be a filamentous phage. The phage may be selected from the class I phages fd, M13, f1, If1, lke, ZJ/Z, Ff and the class II phages Xf, Pf1 and Pf3. The phage may be fd or a derivative of fd. The derivative may be tetracycline resistant. The said sbp member or polypeptide chain thereof may be expressed as a fusion with the gene III capsid protein of phage fd or its counterpart in another filamentous phage. The sbp member or polypeptide chain thereof may be inserted in the N-terminal region of the mature capsid protein downstream of a secretory leader peptide. The sequence may be inserted after amino acid +1 of the mature protein. The site for insertion may be flanked by short sequences corresponding to sequences which occur at each end of the nucleic acid to be inserted.
The host may be E. coli. 
Nucleic acid encoding an sbp member polypeptide may be linked downstream to a viral capsid protein through a suppressible translational stop codon, so that under conditions where the stop is supressed fusion proteins are produced comprising sbp member polypeptide and viral capsid protein, while under non-supressing conditions free form sbp member polypeptides are produced.
Selection systems and assay formats are discussed elsewhere in this text. In these systems and formats, the gene sequence encoding the binding molecule (eg. the antibody) of desired specificity is separated from a general population of rgdps having a range of specifies, by the fact of its binding to a specific target (eg the antigen or epitope). Thus the rgdps formed by said expression may be selected or screened to provide an individual sbp member or a selected mixed population of said sbp members associated in their respective rgdps with nucleic acid encoding said sbp member or a polypeptide chain thereof. The rgdps may be selected by affinity with a member complementary to said sbp member.
Any rgdps bound to said second member may be recovered by washing with an eluant. The washing conditions may be varied in order to obtain rgdps with different binding affinities for said epitope. Alternatively, to obtain eg high affinity rgdps, the complementary member (eg an epitope) may be presented to the population of rgdps (eg pAbs) already bound to a binding member in which case pAbs with a higher affinity for the epitope will displace the already bound binding member. Thus the eluant may contain a molecule which competes with said rgdp for binding to the complementary sbp member. The rgdp may be applied to said complementary sbp member in the presence of a molecule which competes with said package for binding to said complementary sbp member. Nucleic acid derived from a selected or screened rgdp may be used to express said sbp member or a fragment or derivative thereof in a recombinant host organism. Nucleic acid from one or more rgdps may be taken and used to provide encoding nucleic acid in a further said method to obtain an individual sbp member or a mixed population of sbp members, or encoding nucleic acid therefor. The expression end product may be modified to produce a derivative thereof.
A preferred source for the generation of diverse libraries from unimmunised humans is IgM mRNA. It is was found example 43 of WO92/01047 that antibody fragments directed against turkey egg lysozyme and 2-phenyl-5-oxazolone were much more readily isolated from a phage library derived from the IgM mRNA from unimmunised human donors, than from one prepared from IaG mRNA. Furthermore, no 2-phenyl-5-oxazolone binding antibody fragments could be isolated from a library of 2000000 phage antibody clones prepared from IgGmRNA of unimmunised mice (T. Clackson et al, Nature 352 624-628.1991). Examples 1 to 3 of this application show the isolation of antibodies specific for self antigen from the IgM library. Although in these samples, antiself specificities have been selected as single chain Fv fragments in a single replicon format, antibody specificities could be selected as Fab fragments in a single replicon format or in a dual combinatorial, dual replicon format (Hoogenboom et al, 1991 supra) for instance using recombination with the loxP system (PCT/GB92/00883).
Phage libraries may be prepared which are enriched for antibodies directed against self. B lymphocytes express surface IgM and surface IgD before stimulation with antigen but express little soluble IgM or IgD. These unstimulated cells are more likely to contain antibody genes with anti-self specificities. In contrast, terminally differentiated plasma cells which secrete soluble antibodies express little surface immunoglobulin. The preparation of cDNA for phage library preparation using primers which are specific for surface IgM or surface IgD will produce a repertoire of antibody genes enriched for the naive, unselected genes encoding V domains. In B lymphocytes which have been functionally silenced by exposure to self there are greatly reduced levels of surface IgM but unchanged levels of surface IgD (C. C. Goodnow et al. supra). Hence, a primer specific for surface IgD may be particularly suitable for isolation of anti-self antibodies.
However, as demonstrated in this application, IgM mRNA from unselected peripheral blood lymphocytes is one preferred source of V genes for antiself specificities. other sources of such anti-self antibodies may be fetal mRNA or cord blood mRNA (P. M. Lydyard et al Scand J Immunol 31 33-43, 1990).
There is the potential for making repertoires for phage display using the original combination of VH and VL domains by the use of PCR and linkage of the genes encoding them within cells expressing these domains. The principle of xe2x80x98In cell PCRxe2x80x99, where the original VH/VL pairing is maintained, was demonstrated in PCT/GB92/01483 and described in Embleton et al in Nucleic Acids Res., 20, 3831-3837, 1992. This may be particularly useful if lymphocytes can be selected at a stage before the deletion of clones expressing anti-self antibodies.
In one embodiment of this invention, V gene sequences, or even libraries prepared by the synthetic recombination of V, D and J segments may be used. These act as a rich source of anti-self antibodies. In examples 5 to 7, we demonstrate that anti-self specificities against TNF, human anti-rhesus D antibody (OAK3) and human thyroglobulin can be isolated from a phage antibody library prepared by the synthetic joining of V. D and J segments. The use of germ line V genes for this purpose, as shown in examples 5 to 7, should be valuable for the isolation of anti-self antibodies as there is some evidence that B lymphocytes directed against soluble self antigens are functionally silenced and those directed against multivalent membrane bound self antigen are eliminated (S. B. Hartley et al supra; D. M. Russell et al, supra). Thus, the use of synthetic libraries made by VH, DH, JH or VK,JK or VL, JL recombination in vitro or its equivalent may be particularly advantageous for isolation of antibodies directed against multivalent membrane bound self antigens.
In examples 5 to 7 we have used synthetic VH CDR3 segments incorporating sequences of random bases at the V-D-J joining region and linked them to germ line VH gene segments. Other strategies may be used such as making each of the CDR loops of random sequence or making the CDR loops of known canonical structures (C. Chothia et al, Nature 342 877-893, 1989) and incorporating random sequence elements. The germ line nature of the V and J segments could be altered by incorporation of specific or random alterations to the sequence or by using somatically mutated V gene regions. The strategy used in examples 5 to 7 has the advantage that the loop structures of the V gene segments form only a limited number of distinct folds and combinations of folds (C. Chothia et al J. Mol. Biol. 227 779-817, 1992) and have presumably evolved for stability and to create a distribution and range of binding sites well suited to match the structure of antigens. Moreover, the framework regions and first two hypervariable loops of both heavy and light chains of the synthetic human antibodies are likely to be identical in many different individuals. Such synthetic human antibodies could be less immunogenic than entirely artificial structures.
A further but less preferred alternative to the above natural and synthetic phage display libraries would be to prepare random mutagenesis libraries displayed on phage, derived from one or a few human antibody molecules and selecting anti-self antigen specificities from these.
Selection
Individual rgdps eg pAbs expressing the desired specificity for an antigen, can be isolated from a library using the conventional screening techniques (e.g. as described in Harlow, E., and Lane, D., 1988, supra Gherardi, E et al. 1990. J. Immunol. meth. 126 p61-68).
The applicants have also devised selection techniques that are practicable because of the unique properties of rgdps. The general outline of some screening procedures is illustrated in FIG. 5 using pAbs as an example type of rgdp.
The population/library of pAbs to be screened could be generated from immunised or other animals; or be created in vitro by mutagenising pre-existing phage antibodies (using techniques well-known in the art such as oligonucleotide directed mutagenesis (Sambrook, J., et al., 1989 Molecular Cloning a Laboratory Manual, Cold Spring Harbor Laboratory Press) but are preferably derived from unimmunised humans or artificial recombination of human V segments, as described elsewhere. This population can be screened in one or more of the formats described below with reference to FIG. 5, to derive those individual pAbs whose antigen binding properties are different from sample c.
Binding Elution
FIG. 5(i) shows antigen (ag) bound to a solid surface (s) the solid surface (s) may be provided by a petri dish, chromatography beads, magnetic beads and the like. The population/library of pAbs is then passed over the ag, and those individuals p that bind are retained after washing, and optionally detected with detection system d. A detection system based upon anti-fd antisera may be used (see, for instance, Example 4 of WO92/01047). If samples of bound population p are removed under increasingly stringent conditions, the binding affinity represented in each sample will increase. Conditions of increased stringency can be obtained, for example, by increasing the time of soaking or changing the pH of the soak solution, etc.
Competition
Referring to FIG. 5(ii) antigen ag can be bound to a solid support s and bound to saturation by the original binding molecule c. If a population of mutant pAb (or a set of unrelated pAbs) is offered to the complex, only those that have higher affinity for antigen ag than c will bind. In most examples, only a minority of population c will be displaced by individuals from population p. If c is a traditional antibody molecule, all bound material can be recovered and bound p recovered by infecting suitable bacteria and/or by use of standard techniques such as PCR.
An advantageous application is where ag is used as a receptor and c the corresponding ligand. The recovered bound population p is then related structurally to the receptor binding site/and or ligand. This type of specificity is known to be very useful in the pharmaceutical industry.
Another advantageous application is where ag is an antibody and c its antigen. The recovered bound population p is then an anti-idiotype antibody which have numerous uses in research and the diagnostic and pharmaceutical industries.
At present it is difficult to select directly for anti-idiotype antibodies. pAbs would give the ability to do this directly by binding pAb libraries (eg a naive library) to B cells (which express antibodies on their surface) and isolating those phage that bound well.
In some instances it may prove advantageous to pre-select population p. For example, in the anti-idiotype example above, p can be absorbed against a related antibody that does not bind the antigen.
However, if c is a pAb, then either or both c and p can advantageously be marked in some way to both distinguish and select for bound p over bound c. This marking can be physical, for example, by pre-labelling p with biotin; or more advantageously, genetic. For example, c can be marked with an EcoB restriction site, whilst p can be marked with an EcoK restriction site (see Carter, P. et al., 1985, Nucl. Acids Res. 13, 4431-4443). When bound p+c are eluted from the antigen and used to infect suitable bacteria, there is restriction (and thus no growth) of population c (i.e. EcoB restricting bacteria in this example). Any phage that grew, would be greatly enriched for those individuals from p with higher binding affinities. Alternatively, the genetic marking can be achieved by marking p with new sequences, which can be used to specifically amplify p from the mixture using PCR.
Since the bound pAbs can be amplified using for example PCR or bacterial infection, it is also possible to rescue the desired specificity even when insufficient individuals are bound to allow detection via conventional techniques.
The preferred method for selection of a phage displaying a protein molecule with a desired specificity or affinity will often be elution from an affinity matrix with a ligand. Thus, self antigen or fragments thereof may be used to elute specific phage antibodies from self antigen bound to a matrix. Alternatively, the homologous antigen from a different species may be bound to a matrix, a phage antibody library bound, and phage antibodies specific for the self antigen may be eluted using self antigen. For instance, a bovine antigen may be bound to the matrix, a human phage antibody library bound and human antigen used for elution. Antiself antibodies thus isolated will be specific for epitopes shared between the bovine and human antigens. A further but less preferred alternative may be to bind the phage non-specifically to a column and elute with self antigen. For instance, if a Fab phage library is bound to an anti-Fab affinity column, it may be washed at a pH which does not elute non-specific phage and then washed with solution which is the same except it contains self antigen, eluting by virtue of the higher affinity for the mobile phase of phage expressing antibodies against the self antigen.
For each of these formats elution with increasing concentrations of ligand should elute phage displaying binding molecules of increasing affinity. However, when eg a pAb binds to its antigen with high affinity or avidity (or another protein to its binding partner) it may not be possible to elute the pAb from an affinity matrix with molecule related to the antigen. Alternatively, there may be no suitable specific eluting molecule that can be prepared in sufficiently high concentration. In these cases it is necessary to use an elution method which is not specific to eg the antigen-antibody complex. Some of the non-specific elution methods generally used reduce phage viability for instance, phage viability is reduced with time at pH12 (Rossomando, E. F. and Zinder N. D. J. Mol.Biol. 36 387-399 1968). There may be interactions between eg antibodies and affinity matrices which cannot be disrupted without completely removing phage infectivity. In these cases a method is required to elute phage which does not rely on disruption of eg the antibodyxe2x80x94antigen interaction. A method was therefore devised which allows elution of bound pAbs under mild conditions (reduction of a dithiol group with dithiothreitol) which do not disrupt phage structure (Example 47 of WO92/01047).
The method of mild elution uses binding of the phage antibody population to biotinylated antigen and binding to streptavidin magnetic beads. Following washing to remove non-binding phage, the phage antibody is eluted and used to infect cells to give a selected phage antibody population. A disulphide bond between the biotin and the antigen molecule allows mild elution with dithiothreitol. A particularly advantageous way of performing this selection is to use biotinylated antigen in excess but at or below a concentration equivalent to the desired dissociation constant for the antigen-antibody binding. This method is advantageous for the selection of high affinity antibodies (R. E. Hawkins, S. J. Russell and G. Winter J.Mol.Biol. 226 889-896, 1992). Antibodies may also be selected for slower off rates for antigen selection as described in (R. E. Hawkins et al, 1992 supra). The concentration of biotinylated antigen may gradually be reduced to select higher affinity phage antibodies. As an alternative, the phage antibody may be in excess over biotinylated antigen in order that phage antibodies compete for binding, in an analagous way to the competition of peptide phage to biotinylated antibody described by J. K. Scott and G. P. Smith (Science 249 386-390, 1990).
This elution procedure is just one example of an elution procedure under mild conditions. A particularly advantageous method would be to introduce a nucleotide sequence encoding amino acids constituting a recognition site for cleavage by a highly specific protease between the foreign gene inserted, in this instance a gene for an antibody fragment, and the sequence of the remainder of gene III. Examples of such highly specific proteases are Factor X and thrombin. After binding of the phage to an affinity matrix and elution to remove non-specific binding phage and weak binding phage, the strongly bound phage would be removed by washing the column with protease under conditions suitable for digestion at the cleavage site. This would cleave the antibody fragment from the phage particle eluting the phage. These phage would be expected to be infective, since the only protease site should be the one specifically introduced. Strongly binding phage could then be recovered by infecting eg. E. coli TG1 cells.
An alternative procedure to the above is to take the affinity matrix which has retained the strongly bound pAb and extract the DNA, for example by boiling in SDS solution. Extracted DNA can then be used to directly transform E. coli host cells or alternatively the antibody encoding sequences can be amplified, for example using PCR with suitable primers such as those disclosed herein, and then inserted into a vector for expression as a soluble antibody for further study or a pAb for further rounds of selection.
Another preferred method for selection according to affinity would be by binding to an affinity matrix containing low amounts of ligand.
If one wishes to select from a population of phages displaying a protein molecule with a high affinity for its ligand, a preferred strategy is to bind a population of phage to an affinity matrix which contains a low amount of ligand. There is competition between phage, displaying high affinity and low affinity proteins, for binding to the ligand on the matrix. Phage displaying high affinity protein is preferentially bound and low affinity protein is washed away. The high affinity protein is then recovered by elution with the ligand or by other procedures which elute the phage from the affinity matrix (Example 35 of WO92/01047 demonstrates this procedure).
In summary then, for recovery of the packaged DNA from the affinity step, the package can be simply eluted, it can be eluted in the presence of a homologous sbp member which competes with said package for binding to a complementary sbp member; it could be removed by boiling, it could be removed by proteolytic cleavage of the protein; and other methods will be apparent to those skilled in the art eg. destroying the link between the substrate and complementary sbp member to release said packaged DNA and sbp member. At any rate, the objective is to obtain the DNA from the package so that it can be used directly or indirectly, to express the sbp member encoded thereby.
The efficiency of this selection procedure for pAbs and the ability to create very large libraries means that the immunisation techniques developed to increase the proportion of screened cells producing antibodies of interest will not be an absolute requirement. The technique allows the rapid isolation of binding specificities eg antigen-binding specificities, including those that would be difficult or even unobtainable by conventional techniques, for example, catalytic or anti-idiotypic antibodies. Removal of the animal altogether is now possible, once a complete library of the immune repertoire has been constructed.
Applications of Antibodies to Self Antigens
Human antibodies to cell surface components The isolation of such antibody specificities would be particularly useful for preparing agents which mediate cell killing for instance of cancer cells, for example using the natural effector function of antibodies. Anti-self antibodies may also be valuable in the preparation of diagnostic in vivo imaging reagents, for instance using radioisotopes.
Antibodies directed against cell surface components of specific T-cell subsets could be used therapeutically (D. Wraith et al Cell 57 709-715,1989; L. Steinman and R. Mantegazza FASEB J. 4 2726-2731,1990), for instance to prevent T cell action causing rheumatoid arthritis.
Human Antibodies Modifying the Function of Self Molecules
Antibodies can be isolated which modify the action of self molecules such as hormones, growth factors and receptors through their binding to a specific epitope on the molecule. Multifunctional proteins may have both desirable and undesirable characteristics, particularly if they are used therapeutically. For instance, the lymphokine TNF (tumour necrosis factor) binds to, at least two different classes of cell receptors- one commonly found on vascular endothelial cells, the other commonly found on tumour cells. A mouse antibody to TNF has been made which prevents TNF from binding to endothelial cell receptors while still allowing it to bind to tumour cells thus allowing attack on the tumours without toxic side effects mediated through endothelial cells (Patent application PCT/AU90/00337). For therapeutic use of antibody modifiers of hormone or growth factor molecules, it would be preferable to have a human antibody specificity isolated directly through selection from a phage library.
Human Anti-idiotypes
Anti-idiotype antibodies (antibodies directed against the antigen combining sites formed by the variable domains of human antibodies) are conventionally made by isolating an antibody against an antigen and. then using this isolated antibody as an immunogen to raise antibodies directed against it. If the original antibody is directed against a hormone or growth factor, the relationship between antigen and antibody combining sites means that the anti-idiotype may mimic in some aspects the hormone or growth factor and bind to the receptor for these molecules. However, the fraction of anti-idiotype antibodies able to mimic the binding of the hormone to the receptor would be expected to be small. Furthermore, the deletion of antiself lymphocytes would mean that using the conventional route to antiidiotypes would be difficult for the isolation of human anti-idiotype antibodies mimicking molecules binding human receptors. in this application we show that antibodies directed against the antigen combining sites formed by the variable domains of human antibodies may be directly isolated from phage antibody display libraries, as shown in examples 1 and 4, and it should also be possible to identify the anti-idiotypic antibodies mimicking the binding of the hormone directly by screening for binding to the receptor.
Anti-idiotypes may also be useful for the treatment of autoimmune disease. They could be used to bind to circulating autoantibodies. However, it may be preferable to attack directly antibody producing cells, for instance using a bispecific antibody directed against a cell surface marker as well as an anti-idiotype specificity. Alternatively, plasmaphoresis could be used to remove circulating antibody and the cells treated directly.
Human Antibodies Against Receptors
Human antibodies that bind to receptors, blocking or antagonising ligand function could be selected directly fron a phage library displaying antibodies derived from an unimmunised donor.
Human Antibodies to Prevent Transplant Rejection
Antibodies directed against the major histocompatibility complex proteins could be used to treat patients following transplants, or organs prior to transplantation, in order to prevent rejection. Antibodies directed against several lymphocyte cell surface markers have been used for the prevention of rejection in transplants e.g. CD45, CD3, CD4, CD8 and interleukin-2 receptor. Example 3 shows that human antibodies against CD4 can be directly isolated from phage display libraries.
Human Antibodies Against Cytokines
Human antibodies against cytokines would be valuable for treatment of human disease, for example of septic shock with anti-TNF and anti-interleukin 1 antibodies. Examples 1 and 6 show that human antibodies against TNF can be isolated directly from phage antibody libraries derived from unimmunised humans or the synthetic recombination of V,D and J fragments. In many cases these cytokine molecules are strongly conserved between species, for instance transforming growth factor-xcex2 (TGF-xcex2), and it has proved difficult to isolate antibodies directed against the human molecule even in mice. The isolation of human anti-self antibodies as described in this invention provides a method of obtaining human antibodies with such a specificity.
Human Antibodies for Diagnosis and Treatment of Cardiac Disorders
Human antibodies against clot components e.g. fibrin, would be useful for imaging clots when labelled with radioactivity or for dissolving clots, if for example linked to a clot dissolving enzyme such as urokinase.
Antibodies Triggering Receptor Function
Antibodies may be selected that bind to a cell receptor and trigger a biological response in the cell. This is described in more detail below and in Example 8 describes the isolation of such antibodies.
By cycles of growth and selection, those rgdps binding to the cell receptors are isolated. Some of these rgdps encode binding specificities with the potential (alone or in combination with other binding specificities) to trigger the receptors. These binding specificities are tested alone, or in combination, for triggering the cell receptors.
There are a variety of cell receptors in which the binding of a ligand, for example hormone, growth factor, or peptide triggers a biological event, for example the activation of tyrosine kinase activity, or the opening of an ion channel. The rdgps could be selected for binding to cell receptor (or a related receptor with conserved portions of surface such as from another species), for example by using cells displaying the cell receptor, or using soluble receptor immobilised on solid phase, or using domains or peptide epitopes of the receptor. Ideally the receptor would be provided in a crosslinked form (as required for its triggering).
Triggering of receptors at the cell surface often seems to involve the relative movement of proteins or subunits. For example, in the neurotransmitter-gated receptors, the five subunits that are arranged symmetrically in the membrane place, delineate an ion pathway down the centre. Binding of the neurotransmitter is thought to alter the size of the central ion channel by causing small rearrangements between the subunits in an allosteric transition. For tyrosine kinase receptors, the ligand appears to drive receptor oligomerisation. Thus antibodies with binding specificities directed against a receptor may have the potential to promote an allosteric change or to promote oligomerisation. The oligomerisation of the receptors may also be promoted by using bivalent or bispecific antibodies.
The soluble antibodies or antibody fragments may be monovalent fragments, for example, single chain Fv fragments or Fab fragments, or bivalent fragments, for example, Fab2 or complete antibody fragments. The bivalency could also be promoted in other ways, for example (1) by encoding a tag, such as a peptide or protein (for example, the subunit of a dimeric protein) that self associates, at the N or C-terminus of the monomeric fragment, (2) using a bivalent antibody that binds to the monovalent fragment, for example, to a common C-terminal tag, or to an antibody constant domain (3) chemical cross-linking.
Bispecific antibody or bispecific fragments could also be made as for the bivalent fragments. (For expression of the bispecific antibody or fragment in the same cell, the genes encoding both specificities would need to be introduced together). The different antibody xe2x80x9carmsxe2x80x9d could be directed against the same receptor, for example to different epitopes, or to two different receptors (to trigger hybrid receptors).
The direct isolation of anti-self antibodies from phage libraries as described in this invention is important to allow a large number of antibodies to be surveyed for these triggering receptors.
It is appropriate to distinguish the making of antibodies to trigger receptors as is described here and provided as an aspect of the present invention from the xe2x80x9canti-idiotypic routexe2x80x9d in which specific antibodies raised in an animal, including man, by vaccinating the said animal with a specific antigen are themselves used to vaccinate another animal, new antibodies termed anti-idiotypic antibodies (Anti-Ids) being produced able to recognise and bind to the first set of antibodies. Some species of these Anti-Ids are able to mimic the specific biological properties of the original antigen. If for example, the antigen were a peptide hormone or a cell receptor, the Anti-Id to the hormone or cell receptor antigen is able to elicit a response of the cell (See Gaulton, G. N. and Greane, M. I., 1986. Idiotypic mimicry of biological receptors. Ann. Rev. Immunol. 4,253-280; Sege, K. and Peterson, P. A., 1978. Use of anti-idiotypic antibodies as cell surface receptor probes. Proc. Natl. Acad. Sci. Usa. 75, 2443-2447 for examples).
The essence of current teaching of Anti-Ids as mimics of antigens is that they are produced as a result of constructing antibodies to antibodies of the original antigen. There is however, some controversy over whether such anti-idiotypes accurately mimic the original antigen (S. J. Davis et al Nature 358 76-79, 1992).
There is therefore a clear distinction between antibodies prepared by an anti-idiotypic route that mimic antigens such as growth factors or hormones, and antibodies that are made directly to the receptors to trigger the receptors. The antibodies derived by an anti-idiotypic route require the antigen (hormone, growth factor) and will bind to the same epitope on the receptor as the hormone, while the antibodies derived by binding to the receptors need not bind to the same epitope to trigger the receptor. Indeed such antibodies need not mimic a known hormone or growth factor, as their specificity, or binding to receptor (characterised as epitope, on-rate or off-rate) or blood clearance is likely to differ. The process for making the antibodies is also quite different. Anti-idiotypic antibodies are made classically by immunisation of animals, although they can be isolated directly from phage display libraries as described above. Antibodies directed against self receptors are made by selection from V-gene libraries (as described above).
As well as the advantages over the anti-idiotypic route, the antibodies derived directly by receptor binding may even have advantages over the natural hormone or growth factor. Thus receptors that are defective for binding of the natural hormone or growth factor (for example in a genetic disease), may be triggered by an antibody binding at a different epitope.
As therapeutic agents the various isotypes of antibodies or fragments of antibodies carrying the variable regions responsible for the specificity of the molecule have a number of properties having advantages over the bioactive moiety they mimic. For example, unlike the natural hormones their half-life in circulation can be modified readily. Depending on the antibody isotype or fragment chosen, they have half-lives in circulation in a patient ranging from minutes to several weeks. If long term usage or short term clearance is required this can easily be accommodated by choosing the appropriate antibody isotype without need to use slow release devices as implants, or continuous intravenous infusion, etc.
Furthermore, many hormones or tissue growth factors or antigens in general are functionally complex with different epitopes of each of the molecules having various specific functions. Clones of antibody mimics are monofunctional in this respect so could be used to produce one specific biological effect of a hormone without a second effect which latter effect may be disadvantageous to the patient. Thus the lymphokine TNF (tumour necrosis factor) binds to two different classes of cell receptorsxe2x80x94one common on vascular endothelial cells, the other common on tumour cells. If the TNF is modified so that it cannot bind to the endothelial cell receptors but can still bind to tumour cell receptors, the tumours are attacked without at the same time inducing the very toxic side effects mediated through the vascular receptors. (This is described in Australian Patent Application PCT/AU90/00337). An antibody mimic able to recognise the tumour cell receptor would be expected to be very specific and kill tumour cells without inducing toxic side effects mediated through the vascular endothelium since it would have no resemblance to the TNF epitope which binds to receptors on the latter.
Terminology
Much of the terminology discussed in this section has been mentioned in the text where appropriate.
Self
A self antigen is an antigen or epitope which is capable of binding to an antigen binding site formed by antibody variable domain(s) and which is conserved between members of a species of animal and native to the body.
The immune system tries to avoid making antibodies to self antigens. It has been suggested that (i) sequences of germ line V gene segments have been evolved under pressure to be directed towards foreign, e.g. pathogen, antigens and epitopes, and away from being able to provide antibodies which will bind self antigens, and (ii) that, in addition to this, immune tolerance causes those combinations of gene segments encoding anti-self antibody which do arise, to be deleted or anergised. Consequently, there are not normally circulating antibodies against these antigens except in disease states, eg autoimmune diseases. A self antigen may be one which does not vary between individuals of a species. A self antigen may be one for which there is normal allelic variation throughout a population. Immunisation of one individual in a species with a self antigen would not normally be expected to result in generation, or detection, of antibodies to the antigen, except perhaps when tolerance is deliberately broken. Antibodies to a self-antigen may only be present in an individual who is suffering from autoimmune disease. On the other hand, there are some self antigens to which circulating antibodies can be found in a sub-population of normal individuals of a species.
A self antigen may be an antigen recognised by B-cell surface antibodies but not by antibodies which can be found circulating. It might not be possible to detect or obtain circulating antibodies to a self antigen except perhaps when the individual is suffering from an autoimmune disease or syndrome.
An anti-self antibody or antibody fragment is an antibody or fragment thereof which has binding specificity for a self antigen. It may recognise an epitope which is found only on a self antigen, or it may be cross-reactive with an antigen which individuals of the species will recognise as foreign. The present invention is particularly well suited to the production and isolation of antibody fragments which bind only a self antigen.
Specific Binding Pair
This describes a pair of molecules (each being a member of a specific binding pair) which are naturally derived or synthetically produced. One of the pair of molecules, has an area on its surface, or a cavity which specifically binds to, and is therefore defined as complementary with a particular spatial and polar organisation of the other molecule, so that the pair have the property of binding specifically to each other. Examples of types of specific binding pairs are antigen-antibody, biotin-avidin, hotmone-hormone receptor, receptor-ligand, enzyme-substrate, lgG-protein A.
Multimeric Member
This describes a first polypeptide which will associate with at least a second polypeptide, when the polypeptides are expressed in free form and/or expressed on the surface of a substrate. The substrate may be provided by a bacteriophage. Where there are two associated polypeptides, the associated polypeptide complex is a dimer, where there are three, a trimer etc. The dimer, trimer, multimer etc or the multimeric member may comprise a member of a specific binding pair.
Example multimeric members are heavy domains based on an immunoglobulin molecule, light domains based on an immunoglobulin molecule, T-cell receptor subunits.
Replicable Genetic Display Package (Rgdp)
This describes a biological particle which has genetic information providing the particle with the ability to replicate. The particle can display on its surface at least part of a polypeptide. The polypeptide can be encoded by genetic information native to the particle and/or artificially placed into the particle or an ancestor of it. The displayed polypeptide may be any member of a specific binding pair eg. heavy or light chain domains based on an immunoglobulin molecule, an enzyme or a receptor etc.
The particle may be a virus eg. a bacteriophage such as fd or M13.
Package
This describes a replicable genetic display package in which the particle is displaying a member of a specific binding pair at its surface. The package may be a bacteriophage which displays an antigen binding domain at its surface. This type of package has been called a phage antibody (pAb).
Antibody
This describes an immunoglobulin whether natural or partly or wholly synthetically produced. The term also covers any protein having a binding domain which is, or is homologous to, an immunoglobulin binding domain. These proteins can be derived from natural sources, or partly or wholly synthetically produced.
Example antibodies are the immunoglobulin isotypes and the Fab, F(ab1)2, scFv, Fv, dAb, Fd fragments.
Immunoglobulin Superfamily
This describes a family of polypeptides, the members of which have at least one domain with a structure related to that of the variable or constant domain of immunoglobulin molecules. The domain contains two xcex2-sheets and usually a conserved disulphide bond (see A. F. Williams and A. N. Barclay 1988 Ann. Rev Immunol. 6, 381-405).
Example members of an immunoglobulin superfamily are CD4, platelet derived growth factor receptor (PDGFR), intercellular adhesion molecule. (ICAMY. Except where the context otherwise dictates, reference to immunoglobulins and immunoglobulin homologs in this application includes members of the immunoglobulin superfamily and homologs thereof.
Homologs
This term indicates polypeptides having the same or conserved residues at a corresponding position in their primary, secondary or tertiary structure. The term also extends to two or more nucleotide sequences encoding the homologous polypeptides.
Example homologous peptides are the immunoglobulin isotypes and the TIM barrel enzymes.
Functional
In relation to a sbp member displayed on the surface of a rgdp, means that the sbp member is presented in a folded form in which its specific binding domain for its complementary sbp member is the same or closely analogous to its native configuration, whereby it exhibits similar specificity with respect to the complementary sbp member.
Genetically Diverse Population
In connection with sbp members or polypeptide components thereof, this is referring not only to diversity that can exist in the natural population of cells or organisms, but also diversity that can be created by artificial mutation in vitro or in vivo.
Mutation in vitro may for example, involve random mutagenesis using oligonucleotides having random mutations of the sequence desired to be varied. In vivo mutagenesis may for example, use mutator strains of host microorganisms to harbour the DNA (see Example 38 of WO 92/01047). The words xe2x80x9cunique populationxe2x80x9d may be used to denote a plurality of eg polypeptide chains which are not genetically diverse, ie they are all the same. A restricted population is one which is diverse but less so that the full repertoire of an animal or a library, synthetic or otherwise. The diversity may have been reduced by prior selection, eg using antigen binding specificity.
Domain
A domain is a part of a protein that is folded within itself and independently of other parts of the same protein and independently of a complementary binding member. A folded unit is a specific combination of a xcex1-helix and/or xcex2-sheet structure. Domains and folded units contain structures that bring together amino acids that are not adjacent in the primary structure.
Free Form
This describes the state of a polypeptide which is not displayed by a replicable genetic display package.
Conditionally Defective
This describes a gene which expresses a defective polypeptide under one set of conditions, but expresses a different but related non-defective polypeptide under another set of conditions. An example, is a gene containing an amber mutation expressed in non-suppressing or suppressing hosts respectively.
Alternatively, a gene may express a protein which is defective under one set of conditions, but not under another set. An example is a gene with a temperature sensitive mutation.
Suppressible Translational Stop Codon
This describes a codon which allows the translation of nucleotide sequences downstream of the codon under one set of conditions, but under another set of conditions translation ends at the codon. Example of suppressible translational stop codons are the amber, ochre and opal codons.
Mutator Strain
This is a host cell which has a genetic defect which causes DNA replicated within it to be mutated with respect to its parent DNA. Example mutator strains are NR9046mutD5 and NR9046 mut T1 (see Example 38 of WO92/01047).
Helper Phage
This is a phage which is used to infect cells containing a defective phage genome and which functions to complement the defect. The defective phage genome can be a phagemid or a phage with some function encoding gene sequences removed. Examples of helper phages are M13K07, M13K07 gene III no. 3; and phage displaying or encoding a binding molecule fused to a capsid protein.
Vector
This is a DNA molecule, capable of replication in a host organism, into which a gene is inserted to construct a recombinant DNA molecule.
Phage Vector
This is a vector derived by modification of a phage genome, containing an origin of replication for a bacteriophage, but not one for a plasmid.
Phagemid Vector
This is a vector derived by modification of a plasmid genome, containing an origin of replication for a bacteriophage as well as the plasmid origin of replication.
Secreted
This describes a rgdp or molecule that associates with the member of a sbp displayed on the rgdp, in which the sbp member and/or the molecule, have been folded and the package assembled externally to the cellular cytosol.
Repertoire of Rearranged Immunoglobulin Genes
A collection of naturally occurring nucleotides eg DNA sequences which encoded expressed immunoglobulin genes in an animal. The sequences are generated by the in vivo rearrangement of eg V, D and J segments for H chains and eg the V and J segments for L chains. Alternatively the sequences may be generated from a cell line immunised in vitro and in which the rearrangement in response to immunisation occurs intracellularly.
Library
A collection of nucleotides eg DNA sequences within clones; or a genetically diverse collection of polypeptides, or specific binding pair members, or polypeptides or sbp members which are displayed on rgdps capable of being selected or screened to provide an individual polypeptide or sbp member or a mixed population of polypeptides or sbp members.
Repertoire of Artificially Rearranged Immunoglobulin Genes
A collection of nucleotides eg DNA sequences derived wholly or partly from a source other than the rearranged immunoglobulin sequences from an animal. This may include for example, DNA sequences encoding VH domains by combining unrearranged V segments with D and J segments and DNA sequences encoding VL domains by combining V and J segments.
Part or all of the DNA sequences may be derived by oligonucleotide synthesis.
Secretory Leader Peptide
This is a sequence of amino acids joined to the N-terminal end of a polypeptide and which directs movement of the polypeptide out of the cytosol.
Eluant
This is a solution used to breakdown the linkage between two molecules. The linkage can be a non-covalent or covalent bond(s). The two molecules can be members of a sbp.
Derivative
This is a polypeptide which derived from another polypeptide which is encoded by the DNA within a selected rdgp. The derivative polypeptide may differ from the encoded polypeptide by the addition, deletion, substitution or insertion of amino acids, or by the linkage of other molecules to the encoded polypeptide. These changes may be made at the nucleotide or protein level. For example the encoded polypeptide may be a Fab fragment which is then linked to an Fc tail from another source. Alternatively markers such as enzymes, fluoresceins etc may be linked to e.g. Fab, scFv fragments.